QUOTE (Thirty Second Artbomb @ Sep 18 2010, 02:17 AM)
Settings tab, under Campaign Settings, just below Starting Availability Limit. Set the number next to Blackmarket Availability Bonus to 0 if you aren't using that houserule.
I'll note that this particular houserule function appears as early as revision D of the sheet, before there was a separate Settings tab. If you are using older versions of the sheet, you may have to either manually correct all the problem cells, or upgrade to a newer revision.